Arc quenching circuit interrupter



March 24, 1953 c. H. TITUS ARC QUENCHING CIRCUIT INTERRUPTEIR Filed Dec.

Ii venbor Charles H. Titug His Afitprney Patented Mar. 24, 1953 ARC QUENCHING CIRCUIT INTERRUPTER Charles H. Titus, Philadelphia, Pa., assignor to General Electric Company, a corporation of New York Application December 10, 1949, Serial No. 132,258

6 Claims.

The invention relates to arc quenching circuit "interrupters, particular-1y of the type utilizing a barrier structure having one side disposed laterally adjacent the arc terminal conductors in overlapping relation therewith and formed of insulating material subject to the Nernst effect for closely confining and quenching the are produced upon interruption of the circuit.

One object of the invention is to provide an improved spaced-apart strip and intervening slot form of arc-quenching barrier structure that even though formed of material subject to the Nernst effect can adjoin the arc terminal cone 'ductors so as to overlap and extend substantially coextensive with the are drawn therebetween and thereby enable successful are quenching to be obtained while providing a higher dielectric strength under severe arc-quenching conditions and also increase the recovery voltage which the arc terminal conductors of the circuit interrupter will withstand as soon as the arcing resulting from each circuit interruption is quenched.

In quenching a high current electric are an exceedingly high temperature must be overcome, perhaps in excess of 10,000" C. In case such high temperature arc is confined in intimate contact with an insulating arc-quenching barrier plate that adjoins each arc terminal conductors and extends coextensive with the path of the are drawn therebetween, at least the surface of the barrier plate will be raised to a relatively high temperature in the order of a few milliseconds. Since, due to the Nernst effect, most insulating materials suitable for arc-quenching barriers decrease their electrical resistance when heated to a high temperature, it follows that under the extremely high temperature of the electric arc, the resistance across the surface of the insulating arc barrier plate adjacent the arc path may drop from the order of millions of ohms to a relatively few ohms in the order of several milliseconds. After the arc finally is quenched, an increase in resistance across the surface of the arc-quenching barrier plate becomes a function of its temperature decrease. It therefore follows that the thermal time constant of the insulatin barrier material, together with its temperatureresistance characteristic, will determine the rate at which the surfac resistance of the insulating plate can rise following the quenching of the are. Consequently, such rise in surface resistance is not instantaneous and therefore the high temperature surface of the arc-quenching barrier plate will-continue momentarily to act like a current conducting resistor in a path extending'between-the arc terminal conductors or contacts of the circuit interrupter corresponding to the high temperature are path. The resulting sneak current conduction may-produce additional heat-due to the electrical energy which is dissipated in the thin conducting surface path across the insulating plate by the electrical current flowing therethrough between the arc terminal conductors or contacts of the circuit interrupter. Such current-generated added heat in the high tem- .perature surface path of the arc-quenching barrier plate may even cause the temperature of the barrier material in the surface path to further increase "since only the thermal losses from the hot surface will tend to cause the surface temperature to decrease. Thus, a temperature equilibrium point eventually may be reached at which for a given voltage the electricallygenerated heat will balance the thermal losses. Consequently, the arc-quenching insulating barrier plate may continuously remain a current conductor in the high temperature path along its surface and therefore cause the interrupter to fail to interrupt the circuit.

In accordance with the present invention, one or more slots are formed in the arc-quenching insulating barrier plate that is disposed laterally adjacent the arc terminal conductors in overlapping relation therewith so as to extend transverse the high temperature are path for preventing sneak current conduction between the arc terminal conductors after the surface of the barrier plate becomes heated by the high temperature are and the arc is quenched. Preferably a plurality of slots are extended across the high temperature region adjacent the high temperature path of the arc and into the lower temperature regions of the insulating barrier so as to form a plurality of spaced apart trips that serve to break up the relatively low resistance bridging path between the arc terminal conductors or contacts of the circuit interrupter thereby aiding circuit interruption and permitting the interrupter to withstand a, higher circuit recovery voltage for a given current interruptin'g rating. Furthermore, the slots in the barriers cause the expanding gas that passes through the slots to be turbulent, thereby rendering the .gas less conductive by mixing the gas which has been previously cooled with the still hot gas. The slot also render additional surface area on the side of the barrier opposite from the are terminal conductors as well as on the sides of the slots themselves capable of removing heat from the expanding gases.

Although of general application, the improved strip and slot form of arc-quenching insulating barrier structure is particularly advantageous in an intercommunicating multi-slot type of arcquenching circuit interrupter such as disclosed and claimed in the Seaman Patent 2,429,846 that is assigned to the assignee of the present invention. Such improved type of arc-quenching circuit interrupter utilizes multiple pairs of cooperating contacts separable in narrow arcing slots displaced from each other by an are resisting barrier of insulating material with opening-s in the barrier for providing communication between slots to tend to produce a uniform distribution of gases between slot as well as to cause a plurality of parallel arcs to occur, one in each slot.

Thus another object of the invention is to provide an improved form of multi-slot arc quencher having a plurality of insulating barriers formed of insulating material subject to the Nernst eifect and spaced apart to define a plurality of arcing slots and each barrier having a plurality of slots formed therein to extend transverse the high temperature are path for preventing sneak current conduction through the surface of the barrier when it is heated by the arc and further provide a solid spaced apart barrier adjacent each end barrier on the side thereof opposite from the arc terminal conductors to form a restricted lateral expansion space for the arc gases passing through the slots in the end barriers to substantially insulate such are gases from the arc terminal conductors.

Further objects and advantages of the invention will appear in the following description of the accompanying drawing in which Fig. 1 is a front view of one pole of a multi-slot multiple contact circuit interrupter provided with an arc quencher embodying the slotted arc quenching barrier improvements of the present invention. Fig. 2 is a sectional view on line 2-2 of the circuit interrupter and improved arc quencher construction shown in Fig. 1 more clearly showing the parallel arrangement of the slots of progressively variable length in the barrier. Fig. 3 is a sectional View on line 3-3 of multi-slot circuit interrupter shown in Fig. l more clearly showing the restricted space formed outside the end barriers for expansion of the arc gases passing through the slots therein; and Fig. 4 is a perspective view of the preferred form of slotted arc quencher barrier plate embodied in the circuit interrupter shown in Figs. 1, 2, and 3.

As shown in Figs. 1 and 2, the circuit interrupter indicated generally by the reference character I is of the multi-slot multiple contact type described in the above Seaman patent and is provided with a pair of simultaneously movable contact members ll, each having a contact facing l2 for circuit making and breaking engagement with the contact facing l3 carried on the cooperating stationary contact member I4. Each stationary contact member is movably mounted and biased by spring l8 into wiping engagement with the cooperating movable contact I I. The pair of movable circuit interrupting contacts I! are carried in spaced-apart relation on the common operating bar 29 so as to move in the relatively narrow slots 21 formed between the parallel arc quenching barriers 22, 23 and 24, each having a corresponding biased movable stationary contact cooperating therewith as indicated in Fig. 2 so as to jointly interrupt the current in the circuit controlled by the circuit interrupter [0. While not shown it will be understood that the common operating bar 20 may be pivotally mounted and provided with suitable automatic operating mechanism for moving the movable contacts H away from the stationary contacts Hi to interrupt the current flowing through the interrupter under overload conditions.

Each of the improved slotted arc quenching barriers 22, 23, and 24 is formed of suitable molded insulating material subject to the Nernst effect, preferably phospho-asbestos, and overlaps and' thus lies very closely adjacent to or adjoins the relatively movable contacts l2 and 13 so as to extend substantially coextensive with the path of an are drawn therebetween. Therefore, in accordance with the present invention each barrier plate is provided with a series of parallel slots or apertures 26, 27, 28, and 29 of progressively varying length formed in the barrier to extend transverse the path of the are produced upon separation of the movable contact I! from the stationary contact M in order to prevent current conduction therebetween when the surface of the barrier adjacent the arc path is heated to such a temperature that the high resistance property of the insulating material becomes transformed due to the Nernst effect into a relatively low resistance conducting path between the arc terminal conductors as previously pointed out. Each slotted arc barrier is provided with suitable spacing bosses 30 and 3! that project laterally from opposite corners of the barrier on either side thereof so as to act as spacers in assembling the barriers as a unit in the circuit breaker as shown in Fig. 1 with the through clamping bolts 32 and 33 enclosed within the spacers 3t and 32 so as to be isolated from the arc. The stepped projections 35 and 35 enable the back of the arc-quenching barriers to extend on either side of the stationary contact M so as to laterally confine the are produced upon the disengagement of the contact faces l2 and I3. A lateral insulating barrier 4!! extends across the back edge of each of the arc quenching barriers 22, 23, and 24 and engages with the projection 35 so as to form a seal at the back of the upper part of each slot between the barriers and extends beyond each end barrier to engage with the outer solid barrier plates 4| and 42 that form restricted spaces for expansion of the gases passing through the slots in the end barriers Z2 and 24. A similar transverse insulating barrier 45 hooks into a notch 46 formed in each of the barriers so as to seal the lower part of each of the slots between the barriers while permitting ready removal of the arc quenching barrier unit for inspection of the contacts. The transverse barrier 45 is removably secured in position to hold the slotted barrier unit in place by means of the holding-down screws 56 which engage with suitable threaded holes in the bosses or ribs 4'! pro- Jecting from the circuit breaker enclosing casing 48 that preferably is formed of molded insulating material and provided with the notches 49 and the projecting spacer lugs 50 for holding the outer solid barriers ll and 42 in place inside the molded enclosing casing 48 having the removable cover 5| Current is conducted to the stationary contact member M from a threaded front or back connected terminal stud 52 through the current con ductor 53 provided with a flexible conductor loop 54 which produces an electrodynamic force under heavy current conditions tending to aid the biasing spring I8 and maintaining wiping en-;

'ga'gement between the -'contact faces l2 and 13 'during the opening "movement or the circuit interrupter contacts. A protective insulating cov- 'ering 5B of 'suitabl'e 'arc resi'sting material is provided on the outside of the conductor 53.

A mufiler, indicated generally by the reference character 58, extends along the outlet edge of thearoquenching barriers 22, 23, and 24 for-cooling thehigli'lyheatecl gases received from th'e'slots "therebetween during the interruption of the circuit. "Such muffier58 may be-o'fany'suitable type 'but is shown as of the improved type having a plurality of nested zigzag metal plates '59 which is'm'ore ru'u described and claimedin'the patent application, Serial No. 140,414 filed January 25, "1 950jby 'John AIFavre. The'arc gases are'cooled bypassing through the muffler 58 and are then "received into the enlarged terminal connection space 60 and the interval pressure "is vented "through a suitable wire screen 6! inserted in the window '62 formed in the enclosing casing 48. The removable cover 5! of the enclosing casing 43 is provided with a corresponding window 64 for sliding engagement with the wire screen 6 5.

When the movable contact I! is operated to open the circuit under overload conditions, the two contact faces 12 and I 3 are initially maintained in wiping engagement due to the biasing action of spring l8 and also the magnetic biasing action of the current conductor loop 54 until the stationary contact l4 reaches the limit of its bias movement and is stopped by barrier 45. Thereupon the circuit is rapidly opened due to the quick separation of the contact faces [2 and E3 to draw multiple arcs therebetween. The path of :each arcsodrawn extendstra nsverse the slots :26, 27, 28, and 29 formed in each arc-quenching barrierand the magnetic loop action causes each arc to rise in the slots formed between thebarriers toward'the mufller 58. of the zigzag nested plates 59 also serves to draw the arc lengthwise of the slots 25, 21, '28, '29 in :case the "movable contact H has opened far enough to draw the-arc beyondlthe'longest slot 28 before the arc is extinguished depending upon the severity of the overload. In any case, the improved slotted arc quenching barriers 22, 23 and 24 provide a plurality of strips of insulating material closely adjacent each side of the arc path to absorb heat from the arc and thereby quench the are, these strips being the portion of the arc barrier 22 extending between the slots formed therein. However, when the surface temperature of the strips between the slots becomes raised sufiiciently to decrease the resistance of the insulating material to a semi-conducting condition, nevertheless conduction of sneak current between the contacts through the highly heated material of the arc-quenching barriers is effectively prevented by the provision of the plurality of parallel slots in each of the barriers. Thus, as soon as the arc is finally quenched, the circuit interrupter is able to effectively interrupt the circuit even though a relatively high and rapid recovery voltage is impressed between the contacts II and I4.

During the quenching of the arc, the highly heated arc gases pass not only through the nested zigzag plates of the muffler 58 but also laterally through the slots in the end plates 22 and 24 into the restricted expansion spaces 43, 44 formed by the insulating plates 4! and 42 so as to substantially insulate such are gases from the arc terminal conductors. This increases the interrupt ing capacity of the circuit interrupter due to the provision for increased turbulence and more The magnetic action rapid extraction vof the heat from the are :by

the passage of the gases through the islets particularly in the end barriers. Thus, averyirapi'd overall quenching action is obtained due to rapid cooling and condensing of metallic vapors :in the "arc while at the same time reducing-thetamperature of the gases below the point at which they remain conducting.

What I claim as new and desire to-secure by Letters Patent of the United States "is:

'1. In an arc quencher, a pair of relatively m'ovable arc terminal conductors, an arc-quenching barrier formed :of insulating material subject to the Nernst effect and disposed laterallyadjacent in overlapping relation with theconductors to laterally confine and extend substantially coextensive with the path of the are drawn therebetween and having a slot therein extending transverse the high temperature are path to form an insulating gap for preventingsneak current conduction through the surface of the barrier between the arcterminal conductors after the surface of the barrier is heated by the arc and the arc is quenched, and a solid insulating barrier disposed in spaced-apart relation with said slotted arc quenching barrier on the side thereof opposite from said conductors to overlap said slot and provide a restricted lateral expansion space between the opposite side of "the slotted barrier and the spaced-apart solid barrier for arc gases passing through the slot to substantially insulate such gases from the arc terminal conductors.

2. In anarc quencher, a pair of relatively movable arc terminal conductors, an arc quenching barrier formed of insulating material subject to the Nernst effect-and disposed laterally adjacent and in overlapping relation with the conductors to laterally confine and extendsubstantially coextensive with the path of an are drawn therebetween and having a narrow slot extending through the barrier transverse the .arc path with the ends of the slot extending outside the path to form an insulating gap forpreventing sneak current conduction through the surface of the barrier between the arc terminal conductors after the surface of the-barrier is heated by the arc and the arc is quenched, and a solid insulating barrier disposed in spaced-apart relation with said slotted are quenching barrier on the side thereof opposite from said conductors to overlap said slot and provide a restricted lateral expansion space between the opposite side of the slotted barrier and the spaced-apart solid barrier for are gases passing through the slot to substantially insulate such gases from the arc terminal conductors.

3. In an arc quencher, a stationary contact, a cooperating movable circuit interrupting contact, means for contacting and quenching a high temperature are drawn between the contacts including a plurality of strips of insulating material subject to the Nernst eifect disposed in spaced apart alignment laterally adjacent and in overlapping relation with the stationary contact and the path of the movable contact to laterally confine and extend coextensive with and overlap the path of an arc drawn therebetween and provide gaps between the strips transverse the arc path for preventing sneak current conduction between the contacts after the surface of the strips aligned along the arc path is heated by the arc and the arc is quenched, and a solid insulating barrier disposed in spaced-apart relation with said aligned strips on the sides thereof opposite from said contacts to overlap the gaps between the strips and provide a restricted lateral expansion space between the opposite sides of the strips and the barrier for are gases passing through the gaps to substantially insulate such gases from the contacts.

4. In an arc quencher, a pair of relatively movable arc terminal conductors, a pair of juxtaposed arc quenching barrier plates formed cf insulating material subject to the Nernst effect for overlapping the terminal conductors therebetween to laterally confine opposite sides of the path of the arc drawn between the conductors, and each barrier plate having a plurality of slots formed in alignment therein transverse the arc path with the ends of the slots extending outside the path to provide a plurality of insulating gaps for preventing sneak current conduction between the terminal conductors after the surface of each barrier plate is heated by the arc and the arc is quenched, and a solid insulating barrier plate disposed in spaced-apart relation with one of said slotted arc quenching barrier plates on the side thereof opposite from said conductors to overlap said slots and provide a restricted lateral expansion space between the opposite side of the slotted arc quenching barrier and the solid insulating barrier to substantially insulate such gases from the arc terminal conductors.

5. In an arc quencher, a pair of relatively movable arc terminal conductors, a pair of juxtaposed arc quenching barrier plates formed of insulating material subject to the Nernst effect and overlapping the conductors therebetween to laterally confine opposite sides of the path of the are drawn between the conductors and having a plurality of substantially parallel slots of progressively varying length formed in each barrier plate transverse the arc path between the terminal conductors for preventing sneak current conduction therebetween after the surface of each barrier plate is heated by the arc and the arc is quenched, and a solid insulating barrier plate disposed in spaced-apart relation with one of said slotted arc quenching barrier plates on the side thereof opposite from said are terminal conductors to overlap each of said slots and provide a restricted lateral expansion space between the opposite side of the slotted barrier and the solid barrier for are gases passing through the slots to substantially insulate such gases from the arc terminal conductors.

6. A multi-slot arc quencher having in combination a plurality of barrier plates formed of insulating material subject to the Nernst efiect and mounted in spaced apart juxtaposition to form a plurality of slots, a pair of relatively movable arc terminal conductors separable in each intermediate slot for drawing an are therebetween and each intermediate barrier plate having a plurality of narrow elongated apertures formed in parallel alignment therein to establish communication between the adjacent slots and extend transverse the path of the are drawn between the conductors for preventing sneak current conduction between the arc terminal conductors after the surface of each intermediate barrier is heated by the arc and the arc is quenched, and each end barrier plate forming a solid wall overlapping the aligned narrow elongated apertures in the adjacent intermediate barrier plate to provide a restricted lateral expansion space between the Wall and the adjacent intermediate barrier for are gases passing through the apertures to substantially insulate such gases from the arc terminal conductors.

CHARLES H. 'I'ITUS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

